From Sahih Bukhari (Hadith 2527):
Narrated Abu Huraira:The Prophet (ﷺ) said, "Whoever frees his portion of a common slave should free the slave completely by paying the rest of his price from his money if he has enough money; otherwise the price of the slave is to be estimated and the slave is to be helped to work without hardship till he pays the rest of his price
Reference: Bukhari 2527